A stacked structure is formed over a substrate, and the stacked structure has a gate dielectric layer and a floating gate thereon. A first dielectric layer, a second dielectric layer and a third dielectric layer are respectively formed over the top and the sidewalls of the stacked structure and the exposed substrate. A charge storage layer covers over the top and sidewalls of the stacked structure. Also, a pair of auxiliary gates is formed over the substrate beside the charge storage layer, and a gap is between the auxiliary gates and the charge storage layer.